Lexra

Lexra did implement a 32-bit variant of the MIPS architecture. Noteworthy architectural feature was the lack of the MIPS I instructions lwl, lwr, swl and swr that optimize the handling of unaligned loads. Later the LX4580 core added hardware multithreading. Products implementing Lexra's architecture include the LX4080, LX4080P, LX4180, LX4280 and LX5280, LX8000. Today Lexra is a defunct company. Many of the key employees are now working for Ultra Data Corporation located in Waltham, MA on video cores.

Linux support

The instructions lwl, lwr, swl and swr are covered by US patent 4,814,976. Lexra therefore choose to implement these instructions by software emulation. In the 1999 - 2002 lawsuit of MIPS Technologies, Inc. vs. Lexra, Inc. about violation of this and a second patent the court ruled that Lexra's software implementation of these instructions was violating the patent. Which obviously means Linux can't emulate them either.

Technically support for Lexra processors without adding emulation of these instructions would be possible but the question is how much sense it would make as some software may rely on it fairly heavily.

Following the lawsuit Lexra became a MIPS32 license. MIPS later acquired Lexra's IP. This resulted in the end of Lexra's former products and so at this time there also seems to be little interest in actually adding Linux support.

Realtec RTL8181

The Realtec RTL8181 is a highly integrated System-on-a-Chip with a high-performance 32-bit RISC microcontroller, two Ethernet MACs, and a WLAN controller embedded onto a single chip.

The embedded Lexra LX5280 32-bit RISC CPU runs at up to 200MHz and features separate 8KB instruction and data caches.